No restart of Docker daemon after docker.io package is updated

[Claudio Kuenzler]

In our setup using Ubuntu 16.04 Xenial, Rancher as orchestration and docker.io package from the Ubuntu repos, we've already hit twice a problem after the docker.io packages was updated (once manually, once through unattended upgrades).
The first time new containers couldn't be deployed/started anymore and I documented this on the following article:
https://www.claudiokuenzler.com/blog/689/rancher-error-response-from-daemon-dockerd-deleted-no-such-file-or-directory
The second time (discovered a few days ago and fixed today) cross communication between containers on host #1 and containers on host #2 didn't work anymore. thanks to the logs in /var/log/apt/ I saw that an update of docker.io was installed . A manual restart of the Docker daemon solved the problems in both cases.

The root cause seems to be a lack of a "stop" of the Docker daemon in a preinst file followed by a "start" (or a "restart" to keep it simple) of the Docker daemon in a postinst file.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: docker.io 1.12.3-0ubuntu4~16.04.2
ProcVersionSignature: Ubuntu 4.4.0-59.80-generic 4.4.35
Uname: Linux 4.4.0-59-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.5
Architecture: amd64
Date: Tue Feb 28 14:46:05 2017
InstallationDate: Installed on 2016-12-08 (81 days ago)
InstallationMedia: Ubuntu-Server 16.04.1 LTS "Xenial Xerus" - Release amd64 (20160719)
ProcEnviron:
 LANGUAGE=en_US:en
 TERM=xterm
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: docker.io
UpgradeStatus: No upgrade log present (probably fresh install)

[Claudio Kuenzler (napsty)]

Dang! I already opened such a ticket. Please refer to https://bugs.launchpad.net/ubuntu/+source/docker.io/+bug/1658691. Where'd my mind go...?!